In order to evaluate the incidence and causes related to the occurrence of coronary artery restenosis after successful percutaneous transluminal coronary angioplasty (PTCA), 251 consecutive patients, who underwent a successful procedure at either the National Intitutes of Health or Georgetown University Medical Center, were evaluated. Follow-up coronary angiography took place in 83 of the initial group of 89 successful patients one to eleven months after successful PTCA. Restenosis occurred in 32 patients (36%), with all but two patients having either recurring angina and/or a positive exercise test. The other two patients had significant collateral flow to the vessel with restenosis. Conversely, 39 of 41 asymptomatic patients did not have restenosis. For the entire group of 251 successes with follow-up of at least 6 months (average 21 months), 54% was asymptomatic. In the symptomatic group restenosis was found in 63% of patients. Progression of disease in other vessels or presumed coronary vasospasm accounted for symptoms in the remaining patients. Mortality for the entire group was 0.0%. When repeat angioplasy was applied to patients with restenosis, over 80% of the initially successful group were clinically stabilized. There was a lower restenosis rate of 17% for the last 100 successful patients and this observation may be related to higher inflation pressures achieved with newer balloons. No increase mortality was noted with the higher inflation pressures.